There is known a gas-discharge display apparatus such as a plasma display panel (PDP) which includes a transparent first substrate (i.e., a front plate), a second substrate (i.e., a rear plate) that is distant from the front plate by a pre-determined distance and extends parallel to the first plate, a plurality of discharge spaces that are provided in a gas-tight space that is located between the front and rear plates and is filled with a pre-selected gas, and a plurality of pairs of first and second discharge electrodes each pair of which selectively produce a gas discharge in a corresponding one of the discharge spaces, and which utilizes the gas discharge to emit a light from a corresponding one of a plurality of light emission units (i.e., pixels or cells) in the gas-tight space and thereby displays a desired image such as a character, a symbol, or a figure. For example, the gas-discharge display apparatus displays an image by directly utilizing a light such as neon orange that is emitted with the plasma produced by the gas discharge, or utilizing a light that is emitted from a fluorescent body, provided in each light emission unit, when the fluorescent body is excited by an ultraviolet light produced by the plasma. Therefore, a gas-discharge display apparatus of a flat type can be easily increased in size and decreased in thickness and weight. In addition, the gas-discharge display apparatus enjoys a large angle of visibility and a quick response that are comparable to those of a CRT. Thus, the gas-discharge display apparatus is expected to replace the CRT.
Meanwhile, in the conventional gas-discharge display device, generally, the discharge electrodes are formed by using, e.g., a thick-film forming process in which a conductive material is applied to an inner surface of one of the front and rear plates and is subjected to a heat treatment such as firing.
More specifically described, conventional gas-discharge display devices can be grouped into two large groups, i.e., DC types and AC types, with respect to the structure of discharge electrodes. In the DC types, and an AC type having a opposing-discharge structure, discharge electrodes are arranged in two directions perpendicular to each other on the front and rear plates. Generally, the discharge electrodes are each formed of a conductive thick film. In addition, in an AC type having a three-electrode surface-discharge structure, sustaining electrodes are provided on one of the front and rear plates such that the sustaining electrodes extend parallel to each other in one direction; and writing electrodes are provided on the other plate such that the writing electrodes extend in another direction perpendicular to the above-indicated one direction. In the surface discharge structure, the sustaining electrodes that are required to have as high as possible a light transmitting property, are constituted by bus electrodes each of which includes a transparent electrode formed of, e.g., an ITO (indium tin oxide) film and a conductive thick film to compensate for the electrical conductivity of the transparent electrode. In addition, in the AC types, discharge electrodes or sustaining electrodes are covered with a dielectric thick film so as to allow the production of alternating current discharges.
Therefore, in each of the above-described electrode structures, the electrodes are formed on the inner surface of at least one of the front and rear plates (i.e., substrates), by using, e.g., the thick-film forming process in which the substrates are subjected to the heat treatment so as to fire the thick films, and accordingly the substrates may be distorted and the dielectric and conductive thick films may be cracked or deformed.
More specifically described, in the heat treatment of the thick-film forming process, the substrates may be distorted because of the variation of amounts of thermal expansion of each substrate resulting from the distribution of temperatures in the each substrate and/or the difference of respective thermal expansion coefficients of the each substrate and the dielectric and conductive thick films. If the substrates are thus distorted, then they cannot have an appropriate flatness and/or the thick-film patterns cannot have an appropriate accuracy.